O2 concentrator with sieve bed bypass and control method thereof

ABSTRACT

An oxygen concentrator includes one or more adsorbent sieve beds operable to remove nitrogen from air to produce concentrated oxygen gas at respective outlets thereof, a product tank fluidly coupled to the respective outlets of the sieve bed(s), a compressor operable to pressurize ambient air, one or more sieve bed flow paths from the compressor to respective inlets of the sieve bed(s), a bypass flow path from the compressor to the product tank that bypasses the sieve bed(s), and a valve unit operable to selectively allow flow of pressurized ambient air from the compressor along the one or more sieve bed flow paths and along the bypass flow path in response to a control signal. The valve unit may be controlled in response to a command issued by a ventilator based on a calculated or estimated total flow of gas and entrained air or % FiO 2  of a patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims the benefit of U.S. ProvisionalApplication No. 62/851,204, filed May 22, 2019 and entitled “O2CONCENTRATOR WITH SIEVE BED BYPASS AND CONTROL METHOD THEREOF,” theentire contents of which is expressly incorporated herein by reference.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND 1. Technical Field of the Invention

The present disclosure relates generally to oxygen concentrators and,more particularly, to an oxygen concentrator arranged to produce a highoxygen content gas to be delivered to a patient by a ventilator.

2. Description of the Related Art

A wide range of clinical conditions may require some form of ventilationtherapy, whereby the patient's work of breathing is assisted by the flowof pressurized gas from a ventilator to the patient's airway. Theseconditions may include hypoxemia, various forms of respiratoryinsufficiency, and airway disorders. There are also non-respiratory andnon-airway diseases that require ventilation therapy, such as congestiveheart failure and neuromuscular diseases.

To improve the quality of life of many patients who require long-termventilation therapy, ventilation systems have been developed which areminiaturized and portable. Some of these systems, for example, theLife2000® system by Breathe Technologies, Inc., are so lightweight andcompact that in their extended range or stand-alone configurations, theyare wearable by the patient. These systems make use of a source ofpressurized ventilation gas to operate. In the stationary orextended-range configuration, the source of pressurized gas may be astationary compressor unit, which may be kept in a patient's home. Inthe stand-alone configuration, which may be generally used when thepatient is outside the home, the portable, wearable ventilator generallyreceives its ventilation gas from a pressurized gas cylinders or aportable compressor.

Many of the above clinical conditions and other clinical conditions mayalso require or benefit from supplemental oxygen therapy, whereby thegas introduced to the patient's airway is augmented by the presence ofadditional oxygen such that the patient inspires gas having oxygenlevels above atmospheric concentration (20.9% at 0% humidity).Supplemental oxygen therapy involves the patient receiving supplementaloxygen gas from an oxygen gas source, which is typically a compressed orcryogenic oxygen cylinder, or an oxygen gas generator. For many years,patients who wished to be mobile relied on oxygen cylinders. However, inrecent years, miniaturization and improvements in battery technology hasresulted in the development of portable oxygen concentrators.

Portable oxygen concentrators typically operate by pressure swingadsorption (PSA), in which ambient air is pressurized by a compressorand passed through an adsorbent sieve bed. The sieve bed is typicallyformed of a zeolite which preferentially adsorbs nitrogen when at highpressure while oxygen passes through. Once the sieve bed reaches itscapacity to adsorb nitrogen, the pressure can be reduced. This reductionin pressure causes the adsorbed nitrogen to be desorbed so it can bepurged, leaving a regenerated sieve bed that is again ready to adsorbnitrogen. With repeated cycles of this operation, an enriched oxygen gasmay be generated. Typically, portable oxygen concentrators have at leasttwo sieve beds so that at one may operate while the other is beingpurged of the nitrogen and vented. Typical portable oxygen concentratorstoday output an enriched oxygen gas with a purity of around 87-96%oxygen. Among existing oxygen concentrators today which may beconsidered portable (especially by an individual suffering from arespiratory condition), there are generally two types available. Thefirst type, which is larger and heavier, is usually capable ofcontinuous flow delivery. Models of this type typically weigh between5-10 kg, have maximum flow rates of around 5-6 liters per minute orless, and are generally configured with wheels and a handle, oftenmimicking the appearance of a suitcase. The second type are lighterunits more suitable for being carried or worn in a satchel, handbag, ora backpack. Models of this type typically weigh less than 2.5 kg and areusually limited to pulsed delivery modes with maximum flow rates ofaround 2 liters per minute or less.

Portable oxygen concentrators have a substantial cost and convenienceadvantage over pressurized oxygen cylinders, due to the pressurizedoxygen cylinders requiring ongoing refilling or replacement.Additionally, portable oxygen concentrators are considered to besignificantly safer than pressurized oxygen cylinders. This safetyconsideration can have a substantial impact on a patient's quality oflife, because many portable oxygen concentrators have been approved bythe FAA for use by travelers on commercial airlines, whereas oxygencylinders are universally banned on commercial flights. Consequently,patients with pressurized oxygen cylinders must make expensive andtime-consuming preparations with an airline ahead of time, or foregoairline travel entirely.

For patients with conditions where assistance with the work of breathingis not required, supplemental oxygen therapy alone, without ventilationtherapy, may be sufficient. However, for many patients, combinedventilation therapy and supplemental oxygen therapy may be a moreoptimal treatment. In healthy patients, sufficient ventilation toperform the work of breathing may typically require minute ventilationrates of between 5 and 8 L/min while stationary, which may double duringlight exercise, and which may exceed 40 L/min during heavy exercise.Patients suffering from respiratory conditions may require substantiallyhigher rates, and substantially higher instantaneous rates. This isespecially true when these patients are outside the home and requireportability, as at these times such patients are often also involved inlight exercise.

It may thus be seen that patients who would prefer to receive thiscombined mode of treatment are substantially limited, due to the factthat in many cases existing portable oxygen concentrators do not outputgas at pressures and/or volumes high enough to be used with a wearable,portable ventilator without the presence of an additional source ofcompressed gas. As such, when maximum portability is desired, thesepatients must either forego the substantial benefits of a portableoxygen concentrator and return to oxygen cylinders (which may outputoxygen gas at the higher pressures and flow rates required forventilation therapy), or additionally have with them a portablecompressor, with the portable oxygen concentrator, the portablecompressor, and the wearable ventilator interfaced together.

Existing systems and methods that seek to provide a combinedsupplemental oxygen/ventilation system are substantially deficient. Forexample, U.S. Patent Application Pub. Nos. 2017/0340851 and 2018/0001048describe the addition of an accumulator tank downstream of the producttank of an oxygen concentrator, for the stated purpose of providing amore constant flow of product gas to a mechanical ventilator. U.S.Patent Application Pub. No. 2017/0113013 describes the use of producttank pressure and output flow rate measurements to determine whether theoxygen concentrator is fluidly coupled to a ventilator (which may becharacterized by utilization of the oxygen-enriched gas of the oxygenconcentrator in intermittent, spontaneous bursts). If it is, the oxygenconcentrator's valves or pump is controlled to increase or decreaseproduct tank pressure or gas flow rate to meet the supply gasrequirements of the ventilator. Such systems can generally be understoodas being aimed only at satisfying the course demands of the ventilator,such as ensuring that the product tank pressure does not fall below acertain threshold. They have no capability of meeting the specific needsof a patient undergoing ventilation therapy. While U.S. PatentApplication Pub. No. 2017/0113013 contemplates the determination of apatient status indicator, the determination is based solely onmeasurements performed within the concentrator and amounts to no morethan a rough estimation.

BRIEF SUMMARY

The present disclosure contemplates various systems, methods, andapparatuses for overcoming the above drawbacks accompanying the relatedart. One aspect of the embodiments of the present disclosure is anoxygen concentrator including one or more adsorbent sieve beds operableto remove nitrogen from air to produce concentrated oxygen gas atrespective outlets thereof, a product tank fluidly coupled to therespective outlets of the one or more adsorbent sieve beds, a compressoroperable to pressurize ambient air, one or more sieve bed flow pathsfrom the compressor to respective inlets of the one or more adsorbentsieve beds, a bypass flow path from the compressor to the product tankthat bypasses the one or more adsorbent sieve beds, and a valve unitoperable to selectively allow flow of pressurized ambient air from thecompressor along the one or more sieve bed flow paths and along thebypass flow path in response to a control signal.

The valve unit may include one or more ON/OFF valves and the valve unitmay selectively allow flow of pressurized ambient air from thecompressor along the one or more sieve bed flow paths and along thebypass flow path by selectively adjusting a timing of states of the oneor more ON/OFF valves relative to an operation cycle of the one or moreadsorbent sieve beds.

The valve unit may include one or more proportional valves and the valveunit may selectively allow flow of pressurized ambient air from thecompressor along the one or more sieve bed flow paths and along thebypass flow path by selectively adjusting a magnitude of an input to theone or more proportional valves. The valve unit may further selectivelyallow flow of pressurized ambient air from the compressor along the oneor more sieve bed flow paths and along the bypass flow path byselectively adjusting a timing of states of the one or more proportionalvalves relative to an operation cycle of the one or more adsorbent sievebeds.

The oxygen concentrator may further include a controller operable togenerate the control signal. The control signal generated by thecontroller may operate the valve unit to maintain a preset oxygenconcentration in the product tank. The controller may generate thecontrol signal in response to a command issued by a ventilator fluidlycoupled to an outlet of the product tank.

Another aspect of the embodiments of the present disclosure is a systemincluding the above oxygen concentrator and the above ventilator. Theventilator may calculate the preset oxygen concentration based on a userinput oxygen concentration. The ventilator may calculate the presetoxygen concentration further based on a measured ventilation gas outputof the ventilator. The ventilator may calculate the preset oxygenconcentration further based on a measured pressure in a patientventilation interface of the ventilator.

The ventilator may include a flow sensor for measuring a flow of gasexpelled by one or more nozzles of a patient ventilation interfaceconnected to the ventilator, a pressure sensor for measuring a pressurein the patient ventilation interface, and a master controller configuredto issue the command based on the measured flow and the measuredpressure. The master controller may be configured to issue the commandbased on a calculation of a total flow of gas and entrained airdelivered by the ventilator as a function of the measured pressure andthe measured flow. The master controller may be configured to issue thecommand based on a comparison of the measured pressure to a plurality ofmeasurements of total flow of gas and entrained air delivered by theventilator stored in correspondence with a plurality of measurements ofpressure in the patient ventilation interface for the measured flow. Themaster controller may be configured to issue the command based on acomparison of the measured pressure to a plurality of measurements offraction of inspired oxygen % FiO₂ stored in correspondence with aplurality of measurements of pressure in the patient ventilationinterface for the measured flow.

The control signal generated by the controller may operate thecompressor to maintain a preset oxygen concentration in the producttank.

Another aspect of the embodiments of the present disclosure is an oxygenconcentrator including one or more adsorbent sieve beds operable toremove nitrogen from air to produce concentrated oxygen gas atrespective outlets thereof, a product tank fluidly coupled to therespective outlets of the one or more adsorbent sieve beds, a compressoroperable to pressurize ambient air, one or more sieve bed flow pathsfrom the compressor to respective inlets of the one or more adsorbentsieve beds, a bypass compressor operable to pressurize ambient air, thebypass compressor being distinct from the compressor, a bypass flow pathfrom the bypass compressor to the product tank that bypasses the one ormore adsorbent sieve beds, and a controller operable to generate acontrol signal to control the bypass compressor to selectively allowflow of pressurized ambient air from the bypass compressor along thebypass flow path.

Another aspect of the embodiments of the present disclosure is an oxygenconcentrator including one or more adsorbent sieve beds operable toremove nitrogen from air to produce concentrated oxygen gas atrespective outlets thereof, a product tank fluidly coupled to therespective outlets of the one or more adsorbent sieve beds, a compressoroperable to pressurize ambient air, one or more sieve bed flow pathsfrom the compressor to respective inlets of the one or more adsorbentsieve beds, a bypass flow path from an external compressor fluid port tothe product tank that bypasses the one or more adsorbent sieve beds, anda controller operable to generate a control signal to control, via anexternal compressor signal port, an external compressor in fluidcommunication with the external compressor fluid port, the controlsignal selectively allowing flow of pressurized ambient air from theexternal compressor along the bypass flow path.

Another aspect of the embodiments of the present disclosure is a modularsystem including the above oxygen concentrator, an oxygen concentratormodule housing the oxygen concentrator, and a compressor module housingthe external compressor. The oxygen concentrator module and thecompressor module may be detachably attachable to from a single unit.

Another aspect of the embodiments of the present disclosure is a methodfor controlling an oxygen concentrator to meet a patient's ventilationand supplemental oxygen needs at a plurality of activity levels of thepatient. The method may include transitioning the oxygen concentrator toa first configuration in which a first portion of ambient air equal toor greater than no ambient air mixes with concentrated oxygen gas outputby one or more sieve beds of the oxygen concentrator to produce aconcentrator output at a first flow having a first oxygen concentration.The method may further include transitioning the oxygen concentrator toa second configuration in which a second portion of ambient air greaterthan the first portion mixes with the concentrated oxygen gas output bythe one or more sieve beds to produce a concentrator output at a secondflow having a second oxygen concentration, the second flow being greaterthan the first flow and the second oxygen concentration being less thanthe first oxygen concentration.

Another aspect of the embodiments of the present disclosure is a methodfor controlling an oxygen concentrator to meet a patient's ventilationand supplemental oxygen needs at a plurality of activity levels of thepatient. The method may include transitioning the oxygen concentrator toa first configuration in which a first portion of concentrated oxygengas output by one or more sieve beds of the oxygen concentrator, thefirst portion being equal to or greater than no concentrated oxygen gas,mixes with ambient air to produce a concentrator output at a first flowhaving a first oxygen concentration. The method may further includetransitioning the oxygen concentrator to a second configuration in whicha second portion of concentrated oxygen gas output by the one or moresieve beds, the second portion being greater than the first portion,mixes with the ambient air to produce a concentrator output at a secondflow having a second oxygen concentration, the second flow being lessthan the first flow and the second oxygen concentration being greaterthan the first oxygen concentration.

Another aspect of the embodiments of the present disclosure is a methodfor calculating a total flow of gas and entrained air delivered by aventilator to a patient. The method may include storing one or moreconstants in association with each of a plurality of nozzle geometries,measuring a flow of gas expelled by one or more nozzles of a patientventilation interface connected to the ventilator, the one or morenozzles having a nozzle geometry corresponding to one of the pluralityof nozzle geometries, measuring a pressure in the patient ventilationinterface, and calculating the total flow based on the measured flow,the measured pressure, and the one or more constants stored inassociation with the nozzle geometry of the one or more nozzles.

The method may further include transmitting a signal to an oxygenconcentrator based on the calculated total flow.

The method may further include calculating a total inspired tidal volumeby integrating the calculated total flow with respect to time. Themethod may further include transmitting a signal to an oxygenconcentrator based on the calculated total inspired tidal volume.

The method may further include calculating an inspired tidal volume ofthe gas expelled by the one or more nozzles by integrating the measuredflow with respect to time, calculating an inspired tidal volume ofentrained air by integrating an entrained flow with respect to time, theentrained flow being the difference between the calculated total flowand the measured flow, and calculating a fraction of inspired oxygen %FiO₂ of the patient based on the inspired tidal volume of the gasexpelled by the one or more nozzles and the inspired tidal volume ofentrained air. The method may further include transmitting a signal toan oxygen concentrator based on the calculated % FiO₂.

For each of the plurality of nozzle geometries, the associated one ormore constants are stored in a memory disposed in a patient ventilationinterface with a nozzle having that nozzle geometry. Calculating thetotal flow may include reading the one or more constants stored in thepatient ventilation interface connected to the ventilator.

Another aspect of the embodiments of the present disclosure is a methodfor controlling an oxygen concentrator based on a total flow of gas andentrained air delivered by a ventilator to a patient. The method mayinclude measuring a flow of gas expelled by one or more nozzles of apatient ventilation interface connected to the ventilator, measuring apressure in the patient ventilation interface, calculating the totalflow based on the measured flow and the measured pressure, andtransmitting a signal to the oxygen concentrator based on the calculatedtotal flow.

The method may further include calculating a total inspired tidal volumeby integrating the calculated total flow with respect to time. Thetransmitting of the signal may be based on the calculated total inspiredtidal volume.

The method may further include calculating an inspired tidal volume ofthe gas expelled by the one or more nozzles by integrating the measuredflow with respect to time, calculating an inspired tidal volume ofentrained air by integrating an entrained flow with respect to time, theentrained flow being the difference between the calculated total flowand the measured flow, and calculating a fraction of inspired oxygen %FiO₂ of the patient based on the inspired tidal volume of the gasexpelled by the one or more nozzles and the inspired tidal volume ofentrained air. The transmitting of the signal may be based on thecalculated % FiO₂.

Another aspect of the embodiments of the present disclosure is anon-transitory program storage medium on which are stored instructionsexecutable by a processor or programmable circuit to perform operationsfor controlling an oxygen concentrator based on a total flow of gas andentrained air delivered by a ventilator to a patient. The operations mayinclude measuring a flow of gas expelled by one or more nozzles of apatient ventilation interface connected to the ventilator, measuring apressure in the patient ventilation interface, and calculating the totalflow based on the measured flow and the measured pressure.

Another aspect of the embodiments of the present disclosure is aventilator including the above non-transitory program storage medium, aprocessor or programmable circuit for executing the instructions, a flowsensor, and a pressure sensor. Measuring the flow may includecommunicating with the flow sensor, and measuring the pressure mayinclude communicating with the pressure sensor.

Another aspect of the embodiments of the present disclosure is aventilation system including the above ventilator and an oxygenconcentrator connected to the ventilator. The operations may furtherinclude transmitting a signal from the ventilator to the oxygenconcentrator based on the calculated total flow.

The oxygen concentrator may include a controller operable to generate acontrol signal in response to the signal transmitted from theventilator, the control signal generated by the controller selectivelyallowing flow of pressurized ambient air into a product tank of theoxygen concentrator. The control signal generated by the controller mayoperate a valve unit of the oxygen concentrator to maintain a presetoxygen concentration in the product tank according to the signaltransmitted from the ventilator. The control signal generated by thecontroller may operate the valve unit to allow the flow of pressurizedambient air to bypass one or more sieve beds of the oxygen concentrator.The control signal generated by the controller may operate a compressorof the oxygen concentrator to maintain a preset oxygen concentration inthe product tank according to the signal transmitted from theventilator. The control signal generated by the controller may operate acompressor external to the oxygen concentrator to maintain a presetoxygen concentration in the product tank according to the signaltransmitted from the ventilator.

Another aspect of the embodiments of the present disclosure is a methodfor controlling an oxygen concentrator to meet a patient's ventilationand supplemental oxygen needs at a plurality of activity levels of thepatient. The method may include transitioning the oxygen concentrator toa first configuration in which a first portion of ambient air mixes withconcentrated oxygen gas output by one or more sieve beds of the oxygenconcentrator to produce a concentrator output at a first flow having afirst oxygen concentration. The method may further include transitioningthe oxygen concentrator to a second configuration in which a secondportion of ambient air mixes with the concentrated oxygen gas output bythe one or more sieve beds to produce a concentrator output at a secondflow having a second oxygen concentration, the second flow being greaterthan the first flow and the second oxygen concentration being less thanthe first oxygen concentration.

Another aspect of the embodiments of the present disclosure is a methodfor estimating a total flow of gas and entrained air delivered by aventilator to a patient. The method may include storing, for each of aplurality of measurements of a flow of gas expelled by one or morenozzles of a patient ventilation interface connected to the ventilator,a plurality of measurements of total flow in correspondence with aplurality of measurements of pressure in the patient ventilationinterface, measuring a flow of gas expelled by the one or more nozzles,measuring a pressure in the patient ventilation interface, andestimating the total flow based on a comparison of the measured pressureto the plurality of measurements of total flow stored for the measuredflow.

The method may further include transmitting a signal to an oxygenconcentrator based on the estimated total flow.

The method may further include calculating a fraction of inspired oxygen% FiO₂ of the patient based on a percentage of oxygen included in thegas expelled by the one or more nozzles and the estimated total flow.The method may further include transmitting a signal to an oxygenconcentrator based on the calculated % FiO_(2.)

Another aspect of the embodiments of the present disclosure is a methodfor estimating a fraction of inspired oxygen % FiO₂ of a patientreceiving ventilatory support from a ventilator. The method may includestoring, for each of a plurality of measurements of a flow of gasexpelled by one or more nozzles of a patient ventilation interfaceconnected to the ventilator, a plurality of measurements of % FiO₂ incorrespondence with a plurality of measurements of pressure in thepatient ventilation interface, measuring a flow of gas expelled by theone or more nozzles, measuring a pressure in the patient ventilationinterface, and estimating the % FiO₂ of the patient based on acomparison of the measured pressure to the plurality of measurements of% FiO₂ stored for the measured flow.

The method may further include transmitting a signal to an oxygenconcentrator based on the estimated % FiO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 shows an example oxygen concentrator according to an embodimentof the present disclosure;

FIG. 2 shows an example control signal for controlling a valve unit ofthe oxygen concentrator in a case of a bypass flow path including anON/OFF valve;

FIG. 3 shows an example control signal for controlling a valve unit ofthe oxygen concentrator in a case of a bypass flow path including aproportional valve;

FIG. 4 shows an example of an oxygen concentrator for use with adedicated bypass compressor that is a separate, add-on component;

FIG. 5 shows an example modular system including an oxygen concentratormodule and a compressor module;

FIG. 6 shows another example modular system including an oxygenconcentrator module;

FIG. 7 shows an example ventilation system according to an embodiment ofthe present disclosure;

FIG. 8 shows an example operational flow that may be performed, in wholeor in part, by the ventilator;

FIG. 9 shows an example of calculated and measured stagnation pressureof a nozzle at different flows;

FIG. 10 shows an example of calculated and measured characteristicP_(aw)-Q_(T) curves of a nozzle for different flows;

FIG. 11 shows another example operational flow that may be performed, inwhole or in part, by the ventilator; and

FIG. 12 shows another example operational flow that may be performed, inwhole or in part, by the ventilator.

DETAILED DESCRIPTION

The present disclosure encompasses various embodiments of oxygenconcentrators, ventilators, and control systems and methods thereof. Thedetailed description set forth below in connection with the appendeddrawings is intended as a description of several currently contemplatedembodiments and is not intended to represent the only form in which thedisclosed invention may be developed or utilized. The description setsforth the functions and features in connection with the illustratedembodiments. It is to be understood, however, that the same orequivalent functions may be accomplished by different embodiments thatare also intended to be encompassed within the scope of the presentdisclosure. It is further understood that the use of relational termssuch as first and second and the like are used solely to distinguish onefrom another entity without necessarily requiring or implying any actualsuch relationship or order between such entities.

FIG. 1 shows an example oxygen concentrator 100 according to anembodiment of the present disclosure. As shown, a ventilator 200 isarranged to deliver a high oxygen content gas produced by the oxygenconcentrator 100 to a patient 13 via a patient ventilation interface 12.Depending on various factors including, for example, the prescription ofthe patient 13, the patient's activity level, user-adjustable settings,and the state of the patient's breathing in a given moment, theventilator 200 may instruct the oxygen concentrator 100 to produce aspecific flow (e.g. volume flow) of gas having a specific oxygenconcentration. The ventilator 200 may then provide such high oxygencontent gas to the patient 13 via the patient ventilation interface 12such that, taking into account any entrainment of additional ambient airin the patient ventilation interface 12, the patient 13 is provided witha desired degree of assistance to the patient's work of breathing and atarget FiO₂.

In general, in order to produce the high oxygen content gas from ambientair, a compressor 110 of the oxygen concentrator 100 pumps ambient airthrough one or more adsorbent sieve beds 120 that remove nitrogen fromthe pressurized air. The resulting gas having high oxygen concentration(e.g. >90%) flows into a product tank 130 for delivery to the ventilator200. In more detail, a controller 140 of the oxygen concentrator 100 maycontrol a valve unit 150 in order to cyclically bring pressurizedambient air into the sieve bed(s) 120 and exhaust the nitrogen wasteproduct extracted by the sieve bed(s). As shown in FIG. 1, for example,two sieve beds 120 may be provided (e.g. Sieve Bed A and Sieve Bed B)having opposed operation cycles, Sieve Bed A filling the product tank130 with high oxygen content gas at the same time that Sieve Bed B isexhausting nitrogen to ambient and vice versa.

The present disclosure contemplates various ways of modifying and/orsupplementing such processes in order to finely tune the oxygenconcentrator 100 to produce a desired flow of gas at a specific oxygenconcentration. Such an oxygen concentrator 100 may be used together withthe ventilator 200 to meet the changing needs of the patient 13 in realtime.

Referring more closely to the arrangement of valves and conduits of thevalve unit 150, it can be seen that the example oxygen concentrator 100of FIG. 1 provides a first sieve bed flow path 160 a from the compressor110 to an inlet of Sieve Bed A through valve Vi of the valve unit 150and a second sieve bed flow path 160 b from the compressor 110 to aninlet of Sieve Bed B through valve V3 of the valve unit 150. In additionto these sieve bed flow paths 160 a, 160 b, the oxygen concentrator 100further includes a bypass flow path 170 from the compressor 110 to theproduct tank 130 through valve V6 of the valve unit 150 that bypassesthe one or more sieve beds 120. By controlling valve V6, the controller140 may allow pressurized ambient air from the compressor 110 to flowdirectly to the product tank 130 without first passing through the sievebed(s) 120. Such ambient air, which avoids the pressure drop associatedwith the sieve bed(s) 120, may then mix with the high oxygen content gasoutput from the sieve bed(s) 120 in the product tank 130. In comparisonto filling the product tank 130 solely from the sieve bed(s) 120, themixture of ambient air and sieve bed output may accumulate more quicklyin the product tank 130 due to the additional volume of ambient airflowing through the bypass flow path 170, while at the same time havinga lower oxygen concentration. By appropriately controlling the valveunit 150, the controller 140 may selectively control the rate of flowinto the product tank 130 and the oxygen concentration of the resultingproduct gas in order to meet the needs of the ventilator 200.

For example, the compressor of a conventional oxygen concentrator havingno bypass flow path 170 may be required to generate approximately 10times the flow needed at the output of the oxygen concentrator in orderto achieve 93% oxygen concentration. That is, a 2 L/min oxygenconcentrator may need to generate 20 L/min of compressed gas in order toproduce 2 L/min of oxygen. By using the bypass flow path 170, the oxygenconcentrator 100 of the present disclosure may allow for a tradeoffbetween the oxygen concentration delivered and the continuous flow (e.g.minute ventilation) that the oxygen concentrator 100 can deliver. Forexample, instead of delivering 2 L/min of flow, the oxygen concentrator100 may be set to deliver 3.8 L/min of flow with 1.8 L/min of oxygen(via the sieve beds 120) and 2 L/min of ambient air (via the bypassvalve 170). The oxygen concentration of the delivered gas will drop downto roughly 60% but the total flow will increase to 3.8 L/min. Using adownstream ventilator 200 that amplifies this flow with entrained air ata ratio of approximately 3:1, the oxygen concentrator 100 can thusdeliver a minute volume of 11.4 L/min (3*3.8) with a % FiO₂ of about32%. In comparison, when delivering 2 L/min of 93% oxygen, the oxygenconcentrator 100 amplified by the ventilator 200 would only deliver 6L/min (3*2) but at an FiO₂ of 50% to the patient 13. In this way, theoxygen concentrator 100 may produce up to 20 L/min of air (completelybypassing the sieve beds 120), which may then be amplified by theventilator 200 to 60 L/min (20*3) at an FiO₂ of about 21% (the oxygenconcentration of ambient air). This may allow a small oxygenconcentrator 100 to meet the minute level demands of a very activepatient 13. As a patient's activity level goes up, it may be better toprovide more ventilation and less oxygen rather than delivering moreoxygen. By using the bypass flow path 170, the oxygen concentrator 100may vary the total gas output between, for example, 2 L/min and 20L/min, with the oxygen concentration varying accordingly from around 93%to around 21%. The oxygen concentrator 100 may thus act as both acompressor and an oxygen concentrator, with the titration levelscontrollable by the ventilator 200 as described below.

The controller 140 may control the valve unit 150 by generating acontrol signal for controlling the individual valves (e.g. V₁-V₆) of thevalve unit 150. For example, the control signal may be generated inresponse to a command issued by the ventilator 200. In this case, thevalve unit 150 may be controlled according to a master/slave arrangementwith the ventilator 200 functioning as master and the controller 140 oroxygen concentrator 100 functioning as slave. The ventilator 200 mayderive a set point for flow and/or oxygen concentration (e.g. based oninputs such as the prescription of the patient 13, the patient'sactivity level, user-adjustable settings, and the state of the patient'sbreathing as measured by the ventilator 200) and the controller 140 mayappropriately generate the control signal to achieve that set point. Ingenerating the control signal, the controller 140 may further take intoaccount measurements of a pressure sensor 180 and/or an oxygenconcentration sensor 190 fluidly coupled to the outlet of the producttank 130. Such measurements may be fed back to the controller 140 andused as additional inputs along with the set point from the ventilator200. The controller 140 may, for example, function as a proportionalintegral derivative (PID) controller or implement other known controlloop feedback mechanisms.

FIG. 2 shows an example control signal for controlling the valve unit150 in a case where the bypass flow path 170 includes an ON/OFF valveV₆. In the example of FIG. 2, the valve unit 150 is controlled toimplement a three-stage cycle, in which the compressed air from thecompressor 110 is passed through Sieve Bed A in a first stage, passedthrough Sieve Bed B in a second stage, and passed directly to theproduct tank 130 via the ON/OFF valve V₆ and the bypass flow path 170 ina third stage.

FIG. 3 shows an example control signal for controlling the valve unit150 in a case where the bypass flow path 170 includes a proportionalvalve V_(6.) In the example of FIG. 3, the valve unit 150 is controlledto implement a two-stage cycle, in which the compressed air from thecompressor 110 is passed through Sieve Bed A in a first stage and passedthrough Sieve Bed B in a second stage, with the proportional valve V₆all the while controlled to selectively allow a portion of thecompressed air to pass directly to the product tank 130 via the bypassflow path 170.

In the example described with respect to FIGS. 1-3, the bypass flow path170 connects the product tank 130 directly to the compressor 110, thatis, the same compressor 110 that is fluidly coupled to the sieve beds120. However, the disclosed subject matter is not intended to be solimited. For example, the bypass flow path 170 may instead extend from aseparate, dedicated bypass compressor that is distinct from thecompressor 110. Such a dedicated bypass compressor may be turned on andoff or the output (e.g. rpm) of the dedicated compressor may be adjustedaccording to the control signal generated by the controller 140 in orderto selectively allow flow from the dedicated bypass compressor to theproduct tank 150 to achieve the same effect as the valve V₆ of the valveunit 150. In the case of controlling a dedicated bypass compressor inthis way, the valve V₆ may be omitted. The dedicated bypass compressormay be included in the housing of the oxygen concentrator 100 or may bea separate, add-on component whose output is connected to the bypassflow path 170 of the oxygen concentrator 100 via a dedicated connector.

FIG. 4 shows an example of an oxygen concentrator 400 for use with adedicated bypass compressor that is a separate, add-on component asdescribed above. The oxygen concentrator 400 may be the same as theoxygen concentrator 100 described in relation to FIG. 1 and may includea compressor 410, sieve beds 420, product tank 430, controller 440,valve unit 450, sieve bed flow paths 460 a, 460 b, bypass flow path 470,pressure sensor 480, and oxygen concentration sensor 490 that are thesame as the compressor 110, sieve beds 120, product tank 130, controller140, valve unit 150, sieve bed flow paths 160 a, 160 b, bypass flow path170, pressure sensor 180, and oxygen concentration sensor 190 of theoxygen with the following differences. Whereas the bypass flow path 170of FIG. 1 extends from the compressor 110 to the product tank 130, thebypass flow path 470 of FIG. 4 does not extend from the compressor 410to the product tank 430 but rather extends from an external compressorfluid port 472 to the product tank 430. Furthermore, valve V₆ of thevalve unit 150 is omitted in the valve unit 450 and the control signalgenerated by the controller 440 is instead used to control the externalbypass compressor via an external compressor signal port 474. As notedabove, such an external bypass compressor may be turned on and off orthe output of the external compressor may be adjusted according to thecontrol signal in order to achieve the same effect as the valve V₆.

FIG. 5 shows an example modular system 500 including an oxygenconcentrator module 510 and a compressor module 520. The oxygenconcentrator module 510 may house the oxygen concentrator 400 of FIG. 4(e.g. providing 0-2 liters per minute O₂ or 0-20 liters per minute airat 20-30 PSI and having a 100 Wh battery with a 1-2 hour range), withthe compressor module 520 housing the external compressor (e.g.providing 0-10 liters per minute air at 20-30 PSI and having a 100 Whbattery with a 2-3 hour range). As depicted by the large arrows at thetop and bottom of the modular system 500, the oxygen concentrator module510 and compressor module 520 may be detachably attached to form asingle unit. For example, a user may slide the two modules 510, 520together in the direction of the arrows to cause them to lock togetheras a unit with the external compressor fluid port 472 of the oxygenconcentrator module 510 fluidly coupled to a compressed gas output ofthe compressor module 520 and with the external compressor signal port474 of the oxygen concentrator module 510 electrically coupled to asignal input port of the compressor module 520. Sliding the two modules510, 520 in the opposite direction may unlock and separate the modules510, 520, allowing them to be used separately. In this way, the oxygenconcentrator module 510 may be used by patients only requiring oxygentherapy, the compressor module 520 may be used by patients onlyrequiring mechanical ventilation, and the two units combined may be usedby people requiring both oxygen and mechanical ventilation. It isfurther contemplated that the top of the oxygen concentrator module 510or the top of the compressor module 520 (or the combined surface formedby the tops of both the oxygen concentrator module 510 and thecompressor module 520) may serve as a cradle for docking the ventilator200. Likewise, the bottom of the oxygen concentrator module 510 or thebottom of the compressor module 520 (or the combined surface formed bythe bottoms of both the oxygen concentrator module 510 and thecompressor module 520) may serve as an attachment for a supplementarybattery pack.

FIG. 6 shows another example modular system 600 including an oxygenconcentrator module 610. The oxygen concentrator module 610 may housethe oxygen concentrator 100 of FIG. 1 or the oxygen concentrator module400 of FIG. 4. As shown, the modular system 600 may have furthermodularity in the option to attach a supplementary hot-swappable batterypack 620 and/or a Continuous Positive Airway Pressure (CPAP) module 630(e.g. with a 22 mm ISO Taper connector for CPAP use) to the oxygenconcentrator module 610. For example, the top of the oxygen concentrator610 may serve as a cradle for attaching the CPAP module 630 and mayinclude a latch release and electrical contacts. Likewise, the bottom ofthe oxygen concentrator 610 may serve as a cradle for attaching thebattery pack 620 and may include a latch release and electricalcontacts. The oxygen concentrator module 610 may further include a DISSor Quick Connect and a user interface including, for example, an ON/OFFbutton, a battery power indicator, and a wireless ventilator connectionfor the ventilator 200. Such modularity may be in place of or inaddition to the attachment to an external compressor module 520 asdescribed in relation to the modular system 500 of FIG. 5.

In the above examples of the oxygen concentrator 100, 400, 510, 610,selective control of the rate of flow into the product tank 130, 430 andthe oxygen concentration of the resulting product gas is achieved bymeans of a bypass flow path 170, 470 that bypasses the sieve beds 120,420 of the oxygen concentrator 100, 400, 510, 610. However, the presentdisclosure is not intended to be so limited. For example, the controller140, 440 may intentionally “mess up” the timing of the valves of anotherwise conventionally structured oxygen concentrator. In general, thetiming of the valves of an oxygen concentrator is titrated to producethe most efficient extraction of oxygen in the sieve beds. Bycontrolling the compressor 110, 410 and/or valve unit 150, 450 to modifythe timing of the sieve bed cycles, the controller 140, 440 canintentionally prevent the oxygen and nitrogen from having enough time toseparate completely in the sieve beds 120, 420. As a result, the producttank 130, 430 may be filled with a product gas having a reduced oxygenconcentration and may potentially allow for higher flow rates of theproduct gas to the downstream ventilator 200. The controller 140, 440may, for example, reference a lookup table of sub-optimal compressoroutputs and valve control timings that do not achieve the most efficientseparation of oxygen and nitrogen in the sieve beds 120, 420. Using sucha lookup table, the controller 140, 440 may generate a control signal inresponse to a command issued by the ventilator 200 to meet the changingneeds of the patient 13 in real time. In this case, the bypass flow path170, 470 and valve V6 may be omitted.

FIG. 7 shows an example ventilation system 700 according to anembodiment of the present disclosure. As shown, the ventilation system700 may include the ventilator 200 and patient ventilation interface 12placed in flow communication with the patient 13 as depicted in FIGS. 1and 4, along with any of the oxygen concentrator 100, 400, 510, 610 asdescribed in relation to FIGS. 1, 4, 5, and 6, respectively. Theventilator 200 may be arranged to deliver high oxygen content gasproduced by the oxygen concentrator 100, 400, 510, 610 to the patient 13via the patient ventilation interface 12. The patient ventilationinterface 12 may include such devices as a full-face mask or a nasalmask that can be placed in direct gas flow communication with the upperrespiratory tract of the patient 13, i.e., the nasal cavity and/or theoral cavity. The patient ventilation interface 12 may feature, inaddition to one or more nozzles 15 for delivering the high oxygencontent gas to the patient 13, one or more apertures for the entrainmentof additional ambient air for delivery to the patient 13. Examples ofpatient ventilation interfaces 12 having nozzles 15 and entrainmentapertures usable with the present disclosed subject matter can be found,for example, in U.S. Patent Application Pub. No. 2019/0099570, entitled“PATIENT INTERFACE WITH INTEGRATED JET PUMP,” the entire disclosure ofwhich is hereby incorporated by reference, and may include, for example,the Engage, Inspire, and Universal Circuit™ Connector (UCC) patientinterfaces of the Life2000® Ventilation System by Breathe Technologies,Inc. As such, at any given moment, a total flow (e.g. volume flow) Q_(T)of gas and entrained air delivered by the ventilator 200 to the patient13 may be defined as a sum of a nozzle flow Q_(N) of gas expelled by oneor more nozzles 15 of the patient ventilation interface 12 and anentrainment flow Q_(E) of ambient air entrained by the one or morenozzles 15. That is, the total flow Q_(T) may be defined asQ_(T)=Q_(N)+Q_(E). In the case of the Life2000® Ventilation System, theflow Q_(N) may be 5-40 L/min, which may be maintained for a duration ofup to 3.0 seconds, for example.

Depending on various factors including, for example, the prescription ofthe patient 13, the patient's activity level, user-adjustable settings,and the state of the patient's breathing at a given moment, theentrainment flow Q_(E) (and consequently the total flow Q_(T)) may vary,causing the patient's fraction of inspired oxygen % FiO₂ to vary as agreater or lesser amount of ambient air is delivered in proportion tothe high oxygen content gas expelled by the one or more nozzles 15. Bymeasuring the flow Q_(N) of gas expelled by the one or more nozzles 15and the pressure in the patient ventilation interface 12, the ventilator200 may calculate or estimate the total flow Q_(T). The ventilator 200may instruct the oxygen concentrator 100, 400, 510, 610 to produce aspecific flow of gas having a specific oxygen concentration according tothe estimated or calculated total flow Q_(T). The ventilator 200 maythen provide such high oxygen content gas to the patient 13 via thepatient ventilation interface 12 such that, taking into account theentrainment of additional ambient air in the patient ventilationinterface 12, the patient 13 is provided with a desired degree ofassistance to the patient's work of breathing and a target % FiO₂.

The ventilator 200 may include a first inlet port 16 through which thehigh oxygen content gas is provided to the ventilator 200 by the oxygenconcentrator 100, 400, 510, 610. The first inlet port 16 may be incommunication with an inlet filter 24 that removes particulates andother contaminants from the breathing gas that is ultimately deliveredto the patient. The pressure of the high oxygen content gas originatingfrom the oxygen concentrator 100, 400, 510, 610 may be regulated by avalve 26 having a valve inlet port 26 a in gas flow communication withthe inlet filter 24 and a valve outlet port 26 b that is in gas flowcommunication with an outlet port 28 of the ventilator 14. The state ofthe valve 26 may be selectively adjusted to port a desiredvolume/pressure of gas from the oxygen concentrator 100, 400, 510, 610to the patient 13. The actuation of the valve 26 may be governed by acontroller 30 that implements various methods contemplated by thepresent disclosure, as will be described in further detail below.

The flow of breathing gas that is ported through the valve 26 may bepassed through the outlet port 28 to a gas delivery conduit 32 that iscoupled to the aforementioned patient ventilation interface 12. The gasdelivery conduit 32 is may be, for example, a plastic tube having apredetermined inner diameter such as 22 mm or smaller. A pressuredifference may be generated between the patient ventilation interface 12and the output of the valve 26, i.e., the valve outlet 26 a, dependingon the state of respiration of the patient 13.

In order to ascertain such pressure differentials, the ventilationsystem 700 may include dual pressure sensors, including a valve pressuresensor 34 and a patient interface pressure sensor 36. The valve pressuresensor 34 may be disposed within the ventilator 200 and may monitor thepressure at the valve outlet port 26 b. The patient interface pressuresensor 36 may also be physically disposed within the ventilator 200 butin direct gas flow communication with the patient ventilation interface12 over a pressure sensor line 38 that is connected to a sensor inletport 40 of the ventilator 200. When the ventilator 200 is operating, gaspressure within the pressure sensor line 38 as well as the gas conduit32 may be connected to deliver a purge flow to clear the pressure sensorline 38. This can be done through a purge solenoid 42 connected to both.The purge can be continuous or intermittent according to the patient'sbreathing phase or pressure difference between the valve pressure andthe patient interface pressure.

In addition to measuring pressure differentials at the patientventilation interface 12 and the valve output 26b, flow measurements ofthe breathing gas actually output from the valve 26 may be utilized. Tothis end, the ventilator 200 may include a flow sensor 43 that isin-line with the valve 12 and the outlet port 28.

The ventilator 200 may measure the pressure in the patient ventilationinterface 12 and the flow of gas expelled by the one or more nozzles 15of the patient ventilation interface 12. For example, the controller 30may communicate with one or both of a valve pressure sensor 34 and apatient interface pressure sensor 36 to measure the pressure and maycommunicate with the flow sensor 43 to measure the flow. Based on themeasured pressure and flow, the controller 30 may then estimate orcalculate the total flow Q_(T) and/or various other parameters asdescribed in more detail below. To this end, the ventilator 200 mayfurther include a nozzle data storage 31 that may store one or moreconstants in association with each of a plurality of nozzle geometries.During use, the controller 30 may calculate the total flow Q_(T) basedon the measured flow, the measured pressure, and the one or moreconstants stored in association with the nozzle geometry of the one ormore nozzles 15. Based on the calculated total flow Q_(T), thecontroller 30 may further calculate the patient's % FiO₂. The controller30 may continually calculate the total flow Q_(T) and/or % FiO₂ of thepatient 13 in real time as the user's activity level and breathingchanges and as user-adjustable settings of the ventilator 200 aremodified (e.g. using an input 69 such as a touch screen or buttons andan output 62 such as a display).

Based on the calculated total flow Q_(T) and/or the patient's % FiO₂,the controller 30 may instruct the oxygen concentrator 100, 400, 510,610, for example, by causing a signal (e.g. a radio frequency wirelesssignal) to be transmitted from the ventilator 200 to the oxygenconcentrator 100, 400, 510, 610. Upon receipt of the signal from theventilator 200, the oxygen concentrator 100, 400, 510, 610 may adjustthe pressure, flow, and/or oxygen concentration of the high oxygencontent gas that it produces in order to meet the changing needs of thepatient in real time. Such adjustments may be made within the oxygenconcentrator 100, 400, 510, 610 as described above in relation to FIGS.1 and 4. In this way, the ventilator 200 may control the oxygenconcentrator 100, 400, 510, 610 according to a master/slave arrangementwith the ventilator 200 functioning as master and the oxygenconcentrator 100, 400, 510, 610 functioning as slave.

FIG. 8 shows an example operational flow that may be performed, in wholeor in part, by the ventilator 200 in accordance with an embodiment ofthe disclosed subject matter. The operational flow of FIG. 8 may be usedto calculate the total flow Q_(T) from the measured flow Q_(N) (nozzleflow) of gas expelled by one or more nozzles 15 and the measuredpressure P_(aw) (airway pressure) in the patient ventilation interface12. Equivalently, with the flow Q_(N) of gas expelled by one or morenozzles 15 being known, the operational flow of FIG. 8 may be used tocalculate the entrainment flow Q_(E)=Q_(T)−Q_(N) generated by the flowQ_(N) through the nozzle(s) 15, as well as various other valuesderivable therefrom.

In general, entrainment is affected by the pressure downstream of thenozzle, which, in the case of the nozzle(s) 15 of a patient ventilationinterface 12 such as that of the Life2000® system, may be regarded asthe measured pressure P_(aw). When the pressure P_(aw) reaches thestagnation pressure P_(S), the flow Q_(N) through the nozzle(s) 15equals 0 to due to back pressure in the patient's airways and lungs. Thestagnation pressure P_(S) may be used to calculate the total flow Q_(T)as a function of Q_(N) and P_(aw) according to the following equation:

${{Q_{T}\left( {Q_{N},P_{aw}} \right)} = {\left( {1 - \frac{P_{aw}}{P_{S}\left( Q_{N} \right)}} \right)*Q_{N}*c}},$

where the stagnation pressure P_(S) is a function of the flow Q_(N) ofexpelled gas and may be calculated as the quadratic

P _(S)(Q _(N))=a*Q _(N) ² +b*Q _(N)

and a, b, and c are constants that depend on the specific nozzlegeometry. The constants a, b, and c may be determined in advance foreach nozzle geometry by finding the stagnation pressure that a givenflow will generate. In the case of the UCC patient interface of theLife2000® system, a=0.0191 and b=0.3828 to yield the calculatedrelationship shown in FIG. 9 between the pressure P_(aw) at stagnationpressure and the nozzle pressure Q_(N), i.e. the stagnation pressureP_(S) as a function of nozzle flow Q_(N), or P_(S)(Q_(N)). For the UCCpatient interface, c=8, yielding the calculated relationship shown inFIG. 10 between the total pressure Q_(T) and the pressure P_(aw) foreach of a plurality of nozzle flows Q_(N) (5, 10, 20, 30, and 40 L/min).

The operational flow of FIG. 8 may begin with a step 802 of storing oneor more constants in association with each of a plurality of nozzlegeometries. For example, the above constants a, b, and c may be storedfor each of a plurality of nozzle geometries, such as for the Engage,Inspire, and UCC patient interfaces of the Life2000® system. Theseconstants may be stored, for example, in the nozzle data storage 31shown in FIG. 7. Alternatively, the constants may be stored in thepatient ventilation interfaces 12 themselves, such as in a memory (e.g.EEPROM) disposed in a harness thereof, such that each patientventilation interface 12 may store the constants a, b, and c associatedwith its own particular nozzle geometry. This may allow individualnozzles to be calibrated separately from the ventilator 200 to accountfor manufacturing differences between nozzles.

During the treatment of a patient 13 using the ventilation system 700,the operational flow of FIG. 8 may proceed with a step 804 of measuringa flow Q_(N) of gas expelled from one or more nozzles 15 of the patientventilation interface 12 and a step 806 of measuring a pressure Paw inthe patient ventilation interface 12. Measuring the pressure P_(aw) mayinclude communication between the controller 30 and both the valvepressure sensor 34 and the patient interface pressure sensor 36. Forexample, the measured pressure P_(aw) may be defined as the differencebetween the pressure in the patient ventilation interface 12 as measuredby the patient interface pressure sensor 36 and the pressure at thevalve outlet port 26 b as measured by the valve pressure sensor 34. Withthe measured flow Q_(N) and the measured pressure P_(aw) having beenacquired, the operational flow may continue with a step 808 ofcalculating the total flow Q_(T) of gas and entrained air delivered bythe ventilator 200 to the patient 13. For example, the controller 30 maycalculate the total flow Q_(T) based on the measured flow Q_(N) and themeasured pressure P_(aw) along with the stored constants a, b, and cusing the above equations, e.g., by using the constants a and b and themeasured flow Q_(N) to calculate the stagnation pressure P_(S) and thenusing the measured flow Q_(N), the measured pressure P_(aw), thestagnation pressure P_(S), and the constant c to calculate the totalflow Q_(T). In calculating the total flow Q_(T), the controller 30 mayread the constants a, b, and c from the nozzle data storage 31 or, in acase where the constants are stored in a memory of the patientventilation interface 12, the controller 30 may read the constants a, b,and c from the external memory upon connection of the patientventilation interface 12 to the ventilator 200 (e.g. via smart connectorthat downloads the constants to the ventilator 200).

In a step 810, any of various values derivable from the total flow Q_(T)may be calculated, such as one or more inspired tidal volumes. Forexample, a total inspired tidal volume TotV_(t) may be calculated as anintegral of the total flow Q_(T) with respect to time, an inspired tidalvolume NozV_(t) of the gas expelled by the one or more nozzles 15 may becalculated as an integral of the measured flow Q_(N) with respect totime, and/or an inspired tidal volume EntV_(t) of entrained air may becalculated as an integral with respect to time of the entrained flowQ_(E)=Q_(T)−Q_(N). In a step 812, the controller 30 may calculate the %FiO₂ based on the inspired tidal volume of the gas expelled by the oneor more nozzles 15 and the inspired tidal volume of entrained air. Forexample, assuming the gas expelled by the one or more nozzles 15 is 100%oxygen, the % FiO₂ may be calculated as % FiO₂=100(NozV_(t)+0.21EntV_(t))/TotV_(t, where) 21% is the approximate percentage of oxygen inambient air. More generally, for an arbitrary gas expelled by the one ormore nozzles 15 (for example, in a case where the oxygen concentrator100, 400, 510, 610 is controlled to deliver a lower oxygen concentrationas described above), the % FiO₂ may be calculated as %FiO₂=100(NozV_(t)+0.21 EntV_(t))/TotV_(t), where 100× is the percentageof oxygen included in the gas expelled by the one or more nozzles 15.The value X defining the oxygen concentration of the gas supplied fromthe expelled by the one or more nozzles 15 may be determined from theknown oxygen concentration of the gas supplied from the oxygenconcentrator 100, 400, 510, 610, for example, based on thecurrent/previous setpoint issued by the controller 30 and/or ameasurement of the oxygen concentration sensor 190.

Lastly, in a step 814, the controller 30 of the ventilator 200 mayinstruct the oxygen concentrator 100, 400, 510, 610 based on thecalculated total flow Q_(T) or % FiO₂, for example, by causing a signalto be transmitted from the ventilator 200 to the oxygen concentrator100, 400, 510, 610 as described above. Upon receipt of the signal fromthe ventilator 200, the oxygen concentrator 100, 400, 510, 610 mayadjust the pressure, flow, and/or oxygen concentration of the highoxygen content gas that it produces to produce a desired total flowQ_(T) and/or % FiO₂.

In the above example, the constants a, b, and c are stored for eachnozzle geometry. However, it is also contemplated that only the constantc may be stored for each nozzle geometry, with the stagnation pressureP_(S) further being stored for a range of possible flows Q_(N). In acase where the ventilator 200 is designed for use only with a singlenozzle geometry, it may be unnecessary to store any constants at all andstep 802 can be omitted. The total flow Q_(T) can simply be calculatedas a function of the measured flow Q_(N) and the measured pressureP_(aw) without modifying the above equation for different nozzlegeometries.

FIG. 9 shows an example of calculated and measured stagnation pressureof a nozzle at different flows. As explained above, the calculatedrelationship shown in FIG. 9 was generated using the constants a=0.191and b=0.3828 and the above equation for the stagnation pressure P_(S).The other relationship (“Measured cmH20”) shown in FIG. 9 is theexperimental results of measuring the stagnation pressure P_(S) of theUCC patient interface. As can be seen in FIG. 9, the measuredrelationship closely matches the calculated relationship, demonstratingthat there is a quadratic relationship between stagnation pressure P_(S)and nozzle flow Q_(N).

FIG. 10 shows an example of calculated and measured P_(aw)-Q_(T) curvesfor a nozzle at different flows. As explained above, the calculatedrelationships shown in FIG. 10 were generated using the constant c=8 andthe above equation for the total flow Q_(T) as a function of airwaypressure P_(aw) for different nozzle flows Q_(N). The otherrelationships (“Act-5,” “Act-10,” etc.) are the actual experimentalresults of measuring the relationship between the total flow Q_(T) andthe airway pressure P_(aw) for 5, 10, 20, and 40 L/min nozzle flowsQ_(N). As can be seen in FIG. 10, the measured relationships closelymatch the calculated relationships, demonstrating that there is a linearrelationship between airway pressure P_(aw) and total flow Q_(T).

FIG. 11 shows another example operational flow that may be performed, inwhole or in part, by the ventilator 200 in accordance with an embodimentof the disclosed subject matter. In the example of FIG. 11, rather thancalculating the total flow Q_(T) using the constants a, b, and c and therelationship between total flow Q_(T) and stagnation pressure P_(S) asdescribed above, the pre-determined characteristic P_(aw)-Q_(T) curvesfor a given nozzle (or plurality of nozzles) may be stored in advanceand used to estimate the total flow Q_(T) for a measured pressure P_(aw)and nozzle flow Q_(N). The operational flow may begin with a step 1102of storing total flow data, for example, in the nozzle data storage 31of the ventilator 200. By way of example, the total flow data mayinclude the characteristic curves (e.g. the underlying data thereof,which may be stored in table form or as parameterized equations) of FIG.10 for one or more nozzles. As in the case of storing the constants a,b, c, the pre-stored characteristic curves may alternatively be storedin a memory in each patient interface 12, characterizing that particularpatient interface 12. With respect to a given patient interface 12, thenozzle data storage 31 or external memory may store, for each of aplurality of measurements of a flow Q_(N) of gas expelled by the one ormore nozzles 15 of the patient ventilation interface 12 (e.g. Q_(N)=5,10, 20, 30, 40 as shown in FIG. 10), a plurality of measurements oftotal flow Q_(N) in correspondence with a plurality of measurements ofthe pressure P_(aw) in the patient ventilation interface 12.

During the treatment of a patient 13 using the ventilation system 700,the operational flow of FIG. 11 may proceed with a step 1104 ofmeasuring a flow Q_(N) of gas expelled from one or more nozzles 15 ofthe patient ventilation interface 12 and a step 1106 of measuring apressure P_(aw) in the patient ventilation interface 12 as describedabove. With the measured flow Q_(N) and the measured pressure P_(aw)having been acquired, the operational flow may continue with a step 1108of estimating the total flow Q_(T) based on a comparison of the measuredpressure P_(aw) to the plurality of measurements of total flow Q_(T)stored for the measured flow Q_(N). For example, the controller 30 mayreference the nozzle data storage 31 to consult the characteristicPaw-Q_(T) curves shown in FIG. 10, find the characteristic P_(aw)-Q_(T)curve corresponding to the measured flow Q_(N), and read the value ofthe total flow Q_(T) corresponding to the measured pressure P_(aw) alongthat curve.

With the total flow Q_(T) having been estimated as described above, theoperational flow of FIG. 11 may proceed with a step 1110 of calculatingone or more inspired tidal volume(s) or any of various other valuesderivable from the total flow Q_(T), a step 1112 of calculating the %FiO₂ of the patient 13, and a step 1114 of transmitting a signal to theoxygen concentrator 100, all of which can be performed in the same wayas the steps 810, 812, and 814 of the operational flow of FIG. 8. Theonly difference is that, in the case of FIG. 10, the total flow Q_(T)was estimated using pre-stored characteristic curves rather than beingcalculated using the measured pressure P_(aw), the measured flow Q_(N),and one or more constants characterizing the patient interface 12. Uponreceipt of the signal from the ventilator 14, the oxygen concentrator 18may adjust the pressure, flow, and/or oxygen concentration of the highoxygen content gas that it produces to produce a desired total flowQ_(T) and/or % FiO₂.

FIG. 12 shows another example operational flow that may be performed, inwhole or in part, by the ventilator 200 in accordance with an embodimentof the disclosed subject matter. In the example of FIG. 12, rather thanestimating the total flow Q_(T) as a precursor to calculating the % FiO₂of the patient, % FiO₂ data of each nozzle may be stored in advance andused to estimate the % FiO₂ for a measured pressure P_(aw) and nozzleflow Q_(N). The operational flow may begin with a step 1202 of storing %FiO₂ data, for example, in the nozzle data storage 31 of the ventilator200. The % FiO₂ data may include characteristic curves (e.g. theunderlying data thereof, which may be stored in table form or asparameterized equations) for one or more nozzles. As in the case ofstoring the constants a, b, c, the pre-stored characteristic curves mayalternatively be stored in a memory in each patient interface 12,characterizing that particular patient interface 12. With respect to agiven patient interface 12, the nozzle data storage 31 or externalmemory may store, for each of a plurality of measurements of a flowQ_(N) of gas expelled by the one or more nozzles 15 of the patientventilation interface 12 (e.g. Q_(N)=5, 10, 20, 30, 40 as shown in FIG.10), a plurality of measurements of % FiO₂ in correspondence with aplurality of measurements of the pressure P_(aw) in the patientventilation interface 12. Such characteristic P_(aw)-% FiO₂ curves maybe obtained experimentally by measuring % FiO₂ in a laboratory at avariety of pressures P_(aw) and nozzle flows Q_(N) or may be derivedfrom the total flow data described above with respect to the operationalflow of FIG. 11.

During the treatment of a patient 13 using the ventilation system 700,the operational flow of FIG. 11 may proceed with a step 1204 ofmeasuring a flow Q_(N) of gas expelled from one or more nozzles 15 ofthe patient ventilation interface 12 and a step 1206 of measuring apressure P_(aw) in the patient ventilation interface 12 as describedabove. With the measured flow Q_(N) and the measured pressure P_(aw)having been acquired, the operational flow may continue with a step 1208of estimating the patient's FiO₂ based on a comparison of the measuredpressure P_(aw) to the plurality of measurements of FiO₂ stored for themeasured flow Q_(N). For example, the controller 30 may reference thenozzle data storage 31 to consult the % FiO₂ data for the particular oneor more nozzles 15, find the characteristic P_(aw)-% FiO₂ curvecorresponding to the measured flow Q_(N), and read the value of the %FiO₂ corresponding to the measured pressure P_(aw) along that curve.With the patient's % FiO₂ having been estimated as described above, theoperational flow of FIG. 12 may proceed with a step 1210 of transmittinga signal to the oxygen concentrator 100, which can be performed in thesame way as step 814 of FIG. 8 or step 1114 of FIG. 11. The onlydifference is that, in the case of FIG. 12, the % FiO₂ was estimateddirectly using pre-stored characteristic curves rather than beingcalculated from the total flow Q_(T). Upon receipt of the signal fromthe ventilator 14, the oxygen concentrator 18 may adjust the pressure,flow, and/or oxygen concentration of the high oxygen content gas that itproduces to produce a desired entrainment ratio and/or % FiO₂.

The above example operational flows of FIGS. 8, 11, and 12 the totalflow Q_(T) and or patient's % FiO₂ is calculated or estimated and usedto characterize the needs of the patient 13 in a given moment for thepurpose of controlling an oxygen concentrator 100. However, thedisclosed subject matter is not intended to be limited to these specificparameters. For example, various derived or otherwise related parametersmay be used instead, such as the entrainment flow Q_(E), an entrainmentratio η=(Q_(T)−Q_(N))/Q_(N), or the tidal volume TotV_(t), NozV_(t), orEntV_(t). Using the disclosed subject matter, any and all such valuesmay be calculated and/or estimated based on the measured patient airwaypressure P_(aw) and the nozzle flow Q_(N).

The controller 140, 440 of the oxygen concentrator 100, 400 and/or thecontroller 30 of the ventilator 200 and their respective functionalitymay be implemented with a programmable integrated circuit device such asa microcontroller or control processor. Broadly, the device may receivecertain inputs, and based upon those inputs, may generate certainoutputs. The specific operations that are performed on the inputs may beprogrammed as instructions that are executed by the control processor.In this regard, the device may include an arithmetic/logic unit (ALU),various registers, and input/output ports. External memory such asEEPROM (electrically erasable/programmable read only memory) may beconnected to the device for permanent storage and retrieval of programinstructions, and there may also be an internal random access memory(RAM). Computer programs for implementing any of the disclosedfunctionality of the controller 140, 440 and/or controller 30 may resideon such non-transitory program storage media, as well as on removablenon-transitory program storage media such as a semiconductor memory(e.g. IC card), for example, in the case of providing an update to anexisting device. Examples of program instructions stored on a programstorage medium or computer-readable medium may include, in addition tocode executable by a processor, state information for execution byprogrammable circuitry such as a field-programmable gate arrays (FPGA)or programmable logic device (PLD).

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein. Further, the various features of the embodimentsdisclosed herein can be used alone, or in varying combinations with eachother and are not intended to be limited to the specific combinationdescribed herein. Thus, the scope of the claims is not to be limited bythe illustrated embodiments.

What is claimed is:
 1. An oxygen concentrator comprising: one or moreadsorbent sieve beds operable to remove nitrogen from air to produceconcentrated oxygen gas at respective outlets thereof; a product tankfluidly coupled to the respective outlets of the one or more adsorbentsieve beds; a compressor operable to pressurize ambient air; one or moresieve bed flow paths from the compressor to respective inlets of the oneor more adsorbent sieve beds; a bypass flow path from the compressor tothe product tank that bypasses the one or more adsorbent sieve beds; anda valve unit operable to selectively allow flow of pressurized ambientair from the compressor along the one or more sieve bed flow paths andalong the bypass flow path in response to a control signal.
 2. Theoxygen concentrator of claim 1, wherein the valve unit includes one ormore ON/OFF valves and the valve unit selectively allows flow ofpressurized ambient air from the compressor along the one or more sievebed flow paths and along the bypass flow path by selectively adjusting atiming of states of the one or more ON/OFF valves relative to anoperation cycle of the one or more adsorbent sieve beds.
 3. The oxygenconcentrator of claim 1, wherein the valve unit includes one or moreproportional valves and the valve unit selectively allows flow ofpressurized ambient air from the compressor along the one or more sievebed flow paths and along the bypass flow path by selectively adjusting amagnitude of an input to the one or more proportional valves.
 4. Theoxygen concentrator of claim 3, wherein the valve unit selectivelyallows flow of pressurized ambient air from the compressor along the oneor more sieve bed flow paths and along the bypass flow path byselectively adjusting a timing of states of the one or more proportionalvalves relative to an operation cycle of the one or more adsorbent sievebeds.
 5. The oxygen concentrator of claim 1, further comprising acontroller operable to generate the control signal.
 6. The oxygenconcentrator of claim 5, wherein the control signal generated by thecontroller operates the valve unit to maintain a preset oxygenconcentration in the product tank.
 7. The oxygen concentrator of claim6, wherein the controller generates the control signal in response to acommand issued by a ventilator fluidly coupled to an outlet of theproduct tank.
 8. A system comprising: the oxygen concentrator of claim7; and the ventilator.
 9. The system of claim 8, wherein the ventilatorcalculates the preset oxygen concentration based on a user input oxygenconcentration.
 10. The system of claim 9, wherein the ventilatorcalculates the preset oxygen concentration further based on a measuredventilation gas output of the ventilator.
 11. The system of claim 9,wherein the ventilator calculates the preset oxygen concentrationfurther based on a measured pressure in a patient ventilation interfaceof the ventilator.
 12. The system of claim 8, wherein the ventilatorincludes: a flow sensor for measuring a flow of gas expelled by one ormore nozzles of a patient ventilation interface connected to theventilator; a pressure sensor for measuring a pressure in the patientventilation interface; and a master controller configured to issue thecommand based on the measured flow and the measured pressure.
 13. Thesystem of claim 12, wherein the master controller is configured to issuethe command based on a calculation of a total flow of gas and entrainedair delivered by the ventilator as a function of the measured pressureand the measured flow.
 14. The system of claim 12, wherein the mastercontroller is configured to issue the command based on a comparison ofthe measured pressure to a plurality of measurements of total flow ofgas and entrained air delivered by the ventilator stored incorrespondence with a plurality of measurements of pressure in thepatient ventilation interface for the measured flow.
 15. The system ofclaim 12, wherein the master controller is configured to issue thecommand based on a comparison of the measured pressure to a plurality ofmeasurements of fraction of inspired oxygen % FiO₂ stored incorrespondence with a plurality of measurements of pressure in thepatient ventilation interface for the measured flow.
 16. The oxygenconcentrator of claim 5, wherein the control signal generated by thecontroller operates the compressor to maintain a preset oxygenconcentration in the product tank.
 17. A system comprising: one or moreadsorbent sieve beds operable to remove nitrogen from air to produceconcentrated oxygen gas at respective outlets thereof; a product tankfluidly coupled to the respective outlets of the one or more adsorbentsieve beds; a compressor operable to pressurize ambient air; one or moresieve bed flow paths from the compressor to respective inlets of the oneor more adsorbent sieve beds; a bypass compressor operable to pressurizeambient air, the bypass compressor being distinct from the compressor; abypass flow path from the bypass compressor to the product tank thatbypasses the one or more adsorbent sieve beds; and a controller operableto generate a control signal to control the bypass compressor toselectively allow flow of pressurized ambient air from the bypasscompressor along the bypass flow path.
 18. The system of claim 17,comprising: an oxygen concentrator module that houses the one or moreadsorbent sieve beds, the product tank, the compressor, the one or moresieve bed flow paths, the bypass flow path, and the controller; and acompressor module, external to the oxygen concentrator module, thathouses the bypass compressor, wherein the controller provides thecontrol signal to the compressor module via an external compressorsignal port of the oxygen concentrator module, and the bypass flow pathreceives the pressurized ambient air from the bypass compressor via anexternal compressor fluid port of the oxygen concentrator module.
 19. Asystem of claim 18, wherein the oxygen concentrator module and thecompressor module are detachably attachable to from a single unit.
 20. Amethod for controlling an oxygen concentrator to meet a patient'sventilation and supplemental oxygen needs at a plurality of activitylevels of the patient, the method comprising: transitioning the oxygenconcentrator to a first configuration in which a first portion ofambient air equal to or greater than no ambient air mixes withconcentrated oxygen gas output by one or more sieve beds of the oxygenconcentrator to produce a concentrator output at a first flow having afirst oxygen concentration; and transitioning the oxygen concentrator toa second configuration in which a second portion of ambient air greaterthan the first portion mixes with the concentrated oxygen gas output bythe one or more sieve beds to produce a concentrator output at a secondflow having a second oxygen concentration, the second flow being greaterthan the first flow and the second oxygen concentration being less thanthe first oxygen concentration.
 21. A method for controlling an oxygenconcentrator to meet a patient's ventilation and supplemental oxygenneeds at a plurality of activity levels of the patient, the methodcomprising: transitioning the oxygen concentrator to a firstconfiguration in which a first portion of concentrated oxygen gas outputby one or more sieve beds of the oxygen concentrator, the first portionbeing equal to or greater than no concentrated oxygen gas, mixes withambient air to produce a concentrator output at a first flow having afirst oxygen concentration; and transitioning the oxygen concentrator toa second configuration in which a second portion of concentrated oxygengas output by the one or more sieve beds, the second portion beinggreater than the first portion, mixes with the ambient air to produce aconcentrator output at a second flow having a second oxygenconcentration, the second flow being less than the first flow and thesecond oxygen concentration being greater than the first oxygenconcentration.
 22. A method for determining a total flow of gas andentrained air delivered by a ventilator to a patient, the methodcomprising: measuring a flow of gas expelled by one or more nozzles of apatient ventilation interface connected to the ventilator; measuring apressure in the patient ventilation interface; and determining the totalflow based on the measured flow and the measured pressure.
 23. Themethod of claim 22, further comprising: storing one or more constants inassociation with each of a plurality of nozzle geometries, wherein theone or more nozzles has a nozzle geometry corresponding to one of theplurality of nozzle geometries, and wherein said determining the totalflow includes calculating the total flow based on the measured flow, themeasured pressure, and the one or more constants stored in associationwith the nozzle geometry of the one or more nozzles.
 24. The method ofclaim 23, wherein, for each of the plurality of nozzle geometries, theassociated one or more constants are stored in a memory disposed in apatient ventilation interface with a nozzle having that nozzle geometry,and said calculating the total flow includes reading the one or moreconstants stored in the patient ventilation interface connected to theventilator.
 25. The method of claim 22, further comprising transmittinga signal to an oxygen concentrator based on the determined total flow.26. The method of claim 22, further comprising calculating a totalinspired tidal volume by integrating the determined total flow withrespect to time.
 27. The method of claim 26, further comprisingtransmitting a signal to an oxygen concentrator based on the calculatedtotal inspired tidal volume.
 28. The method of claim 22, furthercomprising: calculating an inspired tidal volume of the gas expelled bythe one or more nozzles by integrating the measured flow with respect totime; calculating an inspired tidal volume of entrained air byintegrating an entrained flow with respect to time, the entrained flowbeing the difference between the determined total flow and the measuredflow; and calculating a fraction of inspired oxygen % FiO₂ of thepatient based on the inspired tidal volume of the gas expelled by theone or more nozzles and the inspired tidal volume of entrained air. 29.The method of claim 28, further comprising transmitting a signal to anoxygen concentrator based on the calculated % FiO₂.
 30. A non-transitoryprogram storage medium on which are stored instructions executable by aprocessor or programmable circuit to perform operations for controllingan oxygen concentrator based on a total flow of gas and entrained airdelivered by a ventilator to a patient, the operations comprising:measuring a flow of gas expelled by one or more nozzles of a patientventilation interface connected to the ventilator; measuring a pressurein the patient ventilation interface; and determining the total flowbased on the measured flow and the measured pressure.
 31. A ventilatorcomprising: the non-transitory program storage medium of claim 30; aprocessor or programmable circuit for executing the instructions; a flowsensor; and a pressure sensor, wherein said measuring the flow includescommunicating with the flow sensor, and said measuring the pressureincludes communicating with the pressure sensor.
 32. A ventilationsystem comprising: the ventilator of claim 31; and an oxygenconcentrator connected to the ventilator, wherein the operations furthercomprise transmitting a signal from the ventilator to the oxygenconcentrator based on the determined total flow.
 33. The ventilationsystem of claim 32, wherein the oxygen concentrator includes acontroller operable to generate a control signal in response to thesignal transmitted from the ventilator, the control signal generated bythe controller selectively allowing flow of pressurized ambient air intoa product tank of the oxygen concentrator.
 34. The ventilation system ofclaim 33, wherein the control signal generated by the controlleroperates a valve unit of the oxygen concentrator to maintain a presetoxygen concentration in the product tank according to the signaltransmitted from the ventilator.
 35. The ventilation system of claim 34,wherein the control signal generated by the controller operates thevalve unit to allow the flow of pressurized ambient air to bypass one ormore sieve beds of the oxygen concentrator.
 36. The ventilation systemof claim 33, wherein the control signal generated by the controlleroperates a compressor of the oxygen concentrator to maintain a presetoxygen concentration in the product tank according to the signaltransmitted from the ventilator.
 37. The ventilation system of claim 33,wherein the control signal generated by the controller operates acompressor external to the oxygen concentrator to maintain a presetoxygen concentration in the product tank according to the signaltransmitted from the ventilator.
 38. The method of claim 32, furthercomprising: storing, for each of a plurality of measurements of a flowof gas expelled by one or more nozzles of a patient ventilationinterface connected to the ventilator, a plurality of measurements oftotal flow in correspondence with a plurality of measurements ofpressure in the patient ventilation interface, wherein said determiningthe total flow includes estimating the total flow based on a comparisonof the measured pressure to the plurality of measurements of total flowstored for the measured flow.
 39. A method for estimating a fraction ofinspired oxygen % FiO₂ of a patient receiving ventilatory support from aventilator, the method comprising: storing, for each of a plurality ofmeasurements of a flow of gas expelled by one or more nozzles of apatient ventilation interface connected to the ventilator, a pluralityof measurements of % FiO₂ in correspondence with a plurality ofmeasurements of pressure in the patient ventilation interface; measuringa flow of gas expelled by the one or more nozzles; measuring a pressurein the patient ventilation interface; and estimating the % FiO₂ of thepatient based on a comparison of the measured pressure to the pluralityof measurements of % FiO₂ stored for the measured flow.
 40. The methodof claim 39, further comprising transmitting a signal to an oxygenconcentrator based on the estimated % FiO₂.